The valves are essential elements of internal combustion engines. They permit the operation of the latter by alternating between two positions:
A first, so-called “open” position makes possible exchanges between the interior and the exterior of a cylinder using this valve, for example, to inject a fuel into this cylinder.
A second, so-called “closed” position prevents any exchange between the interior and the exterior of this cylinder, for example, to make possible the compression of injected fuel.
In a classical engine, the valves are actuated by means of relatively complicated mechanical links with the rest of the engine. Engines with electrically controlled valves have recently been developed, and this control makes it possible to choose the opening and closing times at will.
Such a device comprises springs and at least one or two electromagnets, the latter receiving control signals for positioning the valve in the open or closed position.
A known device of this type is shown in FIG. 1. It comprises a coil spring 12 surrounding a rod 14 that is integral with a valve 10 and resting, on the one hand, against a stop 16 that is integral with this rod 14 and, on the other hand, against a stop 18 surrounding an opening 20 of the body of the corresponding cylinder 21.
Another rod 22 carrying a plate 26 made of magnetic material cooperates with the rod 14 (or valve stem). Between the rods 22 and 14 is provided a clearance 24, enabling the rod 22 to slide, even though the rod 14 remains immobile when the rod 22 is in the final position towards the top of FIG. 1.
The plate 26 is installed between two electromagnets 28 and 30 passed through by the rod 22. These two electromagnets 28 and 30 contain a coil each, which is conventionally represented in the cross section of FIG. 1 by two crosses, and a magnetic circuit, 29 and 31, respectively, made of magnetic material. The end 32 of the rod 22, which is opposed to the link 24, cooperates with the first end of another spring 34.
The second end of this spring 34 is fixed to a support 36 that is integral with a chassis 37. The springs 34 and 12 keep the plate 26 equidistant from the two electromagnets 28 and 30 when the latter are not generating a magnetic field. This position can be adjusted by varying the position of the support 36 in relation to the chassis 37.
When the electromagnet 28 is activated, it attracts the plate 26 and the latter comes into contact with a part of the magnetic circuit of this electromagnet 28. This movement leads to a sliding of the rod 22 and of the rod 14—along an axis 27 merged with the axis of these rods—such that the head 38 of the valve 10 is brought to rest on its seat. The valve 10 is then closed.
When the electromagnet 30 is activated, the latter attracts the plate 26, which comes into contact with a part of the magnetic circuit of this second electromagnet, leading the rod 22 and the rod 14 along the axis 27, the head 38 consequently being moved away from its seat. The valve 10 is then in the open position.
The springs 12 and 34 are associated with the movement of the rods 14 and 22, being compressed or slackened according to the movements of the latter, a resonant electromechanical system thus being formed.
In some embodiments, for reasons of saving energy during the maintenance of the valve in the open or closed position, the magnetic circuits 29 and 31 of the electromagnets are of the so-called polarized type, i.e., they comprise a permanent magnet. This permits a magnetic blocking of the plate 26 in the open or closed position, respectively, with zero or low current in the electromagnet 30 or 28, respectively. However, it is consequently necessary to provide a force during the transitions from one position to another because the magnetic force generated by the permanent magnet must be overcome. Such a force is costly in terms of energy.